Our prior work has focused on the molecular mechanisms underlying Drosophila[unreadable]s circadian rhythms. Orthologs of genes initially characterized in Drosophila have now been linked to the control of rhythmic behavior and physiology in vertebrates, including fish, frogs, mice and humans. Here we prose four classes of interdisciplinary investigations of the fly[unreadable]s rhythmic behavior. (1) We will extend a classical genetic screen (chemical mutagenesis) for mutations conferring aberrant activity/rest patterns. An X-chromosomal screen produced several mutant lines with effects on either sleep duration or phase. In future work, we will determine the identity of the affected genes, the cellular and molecular patterns of their expression, and will start a comparable screen on chromosomes 2 and 3. (2) We will characterize a novel, reduced- sleep mutant insomniac. These consistently rest for ~400 min/day, nearly 9 hours less than wild type. We will determine where insomniac is expressed within the brain, wheterh cells expressing insomniac have other roles in organizing sleep, and when insomniac function is required to determine sleep duration. (3) We have discovered that when Drosophila are maintained in a photocycle, period mRNA undergoes daily cycles of polyadenylation. The time of polyadenylation can be delayed by prolonged exposure to light. We will determine whether these responses provide a novel mechanism for day- length (seasonal) measurement.